Crown Audio 133472-1A manual Solving Input Problems, Radio Frequencies RF, Hum and Buzz

Input Wiring Tips

1. For all input connectivity, use shielded wire only. Cables with a foil wrap shield or a high-density braid are superior. Cables with a stranded spiral shield, although very fl exible, will break down over time and cause noise problems.

2. Try to avoid using unbalanced lines with professional equipment. If you have no choice, keep the cables as short as possible (see “Balanced vs. Unbalanced” on the next page).

3. To minimize hum and crosstalk, avoid running low-level input cables, high-level output wires and AC power feeds in the same path. Try to run differing signal-cable paths at 90°

Chapter 1: Crown Amplifiers In-Depth

9

to one another. If you must use a common path for all cables, use a star-quad cable for the low-level signals.

4.Before changing input connec- tors or wiring, turn the amplifi er level controls all the way down (counter- clockwise).

5.Before changing output connec- tions, turn the amplifi er level down and the AC power off to minimize the chance of short-circuiting the output.

1.2.2 Solving Input Problems

Infrasonic (Subaudible) Frequencies

Sometimes large infrasonic (sub- audible) frequencies are present in the input signal. These can damage loudspeakers by overloading or overheating them. To attenuate such frequencies, place a capacitor in series with the input signal line. The graph in Figure 1.3 shows some capacitor values and how they affect the frequency response. Use only low-leakage paper, mylar or tantalum

capacitors.

Radio Frequencies (RF)

Figure 1.3

Subsonic Filter Capaci- tor Values

Figure 1.4

Unbalanced RFI Filters

Another problem to avoid is the presence of large levels of radio frequencies or RF in the input signal. Although high RF levels may not

pose a threat to the amplifi er, they

can burn out tweeters or other loads that are sensitive to high frequen- cies. Extremely high RF levels can

also cause your amplifi er to prema-

turely activate its protection circuitry, resulting in ineffi cient operation. RF

can be introduced into the signal chain from many sources such as

local radio stations, tape recorder bias and digital signal processors (DSP). To prevent high levels of input RF, install an appropriate low-pass fi lter in series with the input signal.

Some examples of unbalanced wiring for low-pass fi lters are shown in Figure 1.4.

For balanced input wiring use one of the examples in Figure 1.5. Filters A, B and C correspond to the unbalanced fi lters above. Filter D also incorporates the infrasonic fi lter described previ- ously.

Hum and Buzz

If you have noticeable hum or buzz

in your system, you may want to

check your cable connections to

see if the unwanted noise is being

introduced via a ground loop. To

determine the proper wiring, fi rst

check whether the output from

your source is unbalanced or bal-

anced (if you don’t know, refer to

the unit’s back panel or Operation

Manual). Next, determine if the source’s power cable is fl oating

(ungrounded, 2-prong) or grounded (3-prong). Finally, if the source in unbalanced, check the type of wiring: twin-lead or single coax. Once you have determined the wiring scheme and

cable type, refer to the applicable wiring diagram in Section 1.2.1.

Amplifier Application Guide